Effect of Thermal Deformation Treatment Regimes on Al-4.5Zn-4.5Mg-1Cu-0.12Zr-0.1Sc Alloy Structure and Properties

The microstructure and change in strength of Al-4.5%Zn-4.5%Mg-1%Cu-0,12%Zr-0,1%Sc alloy during annealing after hot deformation in the temperature range 300-450 degrees C are studied. It is established that recrystallization hardly occurs during annealing: at temperatures of 350 degrees C and 400 degrees C softening does not occur, which microstructural studies confirm. During annealing at 450 degrees C yield strength is reduced by increasing the proportion of recrystallized volume to 15%. The structure formed after hot and cold rolling and subsequent annealing has a significant effect on sheet ageing kinetics compared with an ingot. The maximum effect of ageing in the sheet is observed after treatment at 125 degrees C, whereas similar strengthening is achieved in an ingot at 150 degrees C. Test alloy after hot and cold rolling, quenching and ageing at 125 degrees C for 28 hours exhibits a high level of mechanical properties: yield strength 480 +/- 5 MPa; ultimate strength 545 +/- 7 MPa; relative elongation 6.3 +/- 0.4%.

Automated summary

The microstructure and strength changes of Al-4.5%Zn-4.5%Mg-1%Cu-0,12%Zr-0,1%Sc alloy during annealing after hot deformation at temperatures ranging from 300 to 450 degrees C were investigated. Recrystallization hardly occurred during annealing, and softening was not observed at 350 and 400 degrees C, as confirmed by microstructural studies. Annealing at 450 degrees C resulted in a reduction of yield strength due to an increased proportion of recrystallized volume. The structure formed through hot and cold rolling, as well as subsequent annealing, had a significant impact on sheet ageing kinetics compared to an ingot.